Plant virus movement proteins originated from jelly-roll capsid proteins

Numerous, diverse plant viruses encode movement proteins (MPs) that aid the virus movement through plasmodesmata, the plant intercellular channels. MPs are essential for virus spread and propagation in distal tissues, and several unrelated MPs have been identified. The 30K superfamily of MPs (named after the molecular mass of tobacco mosaic virus (TMV) MP, the classical model of plant virology) is the largest and most diverse MP variety, represented in 16 virus families, but its evolutionary origin remained obscure. Here, we show that the core structural domain of the 30K MPs is homologous to the jelly-roll domain of the capsid proteins (CPs) of small RNA and DNA viruses, in particular, those infecting plants. The closest similarity was observed between the 30K MPs and the CPs of the viruses in the families Bromoviridae and Geminiviridae. We hypothesize that the MPs evolved via duplication or horizontal acquisition of the CP gene in a virus that infected an ancestor of vascular plants, followed by neofunctionalization of one of the paralogous CPs, potentially through the acquisition of unique N- and C-terminal regions. During the subsequent coevolution of viruses with diversifying vascular plants, the 30K MP genes underwent explosive horizontal spread among emergent RNA and DNA viruses, likely permitting viruses of insects and fungi that coinfected plants to expand their host ranges, molding the contemporary plant virome.

Automated summary

Many plant viruses encode movement proteins (MPs) that help them move through plant channels called plasmodesmata. The 30K superfamily of MPs is the largest and most diverse variety, represented in 16 virus families, but its origin was unclear. This study found that the core structural domain of the 30K MPs is similar to the capsid proteins (CPs) of small RNA and DNA viruses infecting plants, specifically in the families Bromoviridae and Geminiviridae. The researchers hypothesize that the MPs evolved through the duplication or horizontal acquisition of the CP gene in a virus that infected an ancestor of vascular plants.